The present invention relates generally to apparatus for coupling spacecraft, and more particularly to a berthing apparatus having a construction which permits edge-on contact with a corresponding berthing apparatus so as to minimize the mechanical complexity and weight of the apparatus.
Spacecraft coupling apparatus provide a practical means for the mechanical joining of spacecraft for the logistical support and transfer through the coupling apparatus of crew members, for the mutual support of two or more spacecraft by a sharing of their individual facilities and capabilities, or to enable the on-orbit assembly of spacecraft. Other on-orbit operations that require spacecraft to be joined include the structural expansion of spacecraft, the addition or exchange of modules containing expendable supplies and equipment needed for space-borne experiments and manufacturing processes, and the on-orbit repair and maintenance of spacecraft. Many of these operations are best implemented by crew members moving between the spacecraft through a passage extending between the coupling apparatus in what is known as a shirt-sleeve environment, that is, in a pressurized, earth-like environment. The use of a properly designed coupling apparatus allows unrestricted passage of the crew between spacecraft without the need for cumbersome, restrictive pressure suits or potentially hazardous extravehicular maneuvers.
Spacecraft can be coupled to one another in one of two ways: docking and berthing. In both processes, the interfacing surfaces of coupling apparatus carried by the respective spacecraft must be fully coupled, or superimposed, by a force applied to the spacecraft. Docking and berthing differ in the manner in which the force is applied to the spacecraft. In docking, the coupling force arises from the momentum imparted to the spacecraft by propulsion means such as thrusters on one or both of the spacecraft. One or more alignment guides can be provided to facilitate rotational (clocking) alignment of the interface surfaces of the respective coupling apparatus. Because it is difficult to bring together two spacecraft in a manner such that their interface surfaces are properly rotationally aligned and superimpose completely upon initial contact, the spacecraft interfaces are typically at a slight angle when their leading edges first touch. Therefore, the kinetic energy associated with the relative velocity of the spacecraft must be sufficiently great so as to permit for the correction of slight rotational misalignment and complete superposition of the respective docking interfaces. Because the kinetic energy of the spacecraft is exhausted upon contact of the respective docking interfaces, insufficient relative velocity results in incomplete docking interface superposition and, therefore, a failed docking maneuver.
In contrast to docking, berthing provides a coupling procedure in which one spacecraft is joined to another by the force and directional control applied by an external positioning system, typically comprising a remotely controllable manipulator arm carried by one of the two spacecraft to be joined. The positioning system aligns and guides the interface surface of one spacecraft onto the interface surface of the other to permit spacecraft coupling. Unlike docking, the kinetic energy associated with the spacecraft incident to berthing is not exhausted upon initial contact of the respective interface surfaces. Instead, kinetic energy can be continuously exerted by the positioning system to effect optimal clocking alignment and spacecraft re-positioning until spacecraft coupling has been attained. Because of the comparatively smaller relative velocities and momentums associated with berthing as opposed to docking procedures, berthing mechanisms can be constructed to be less complex and lighter in weight than docking mechanisms constructed to effect coupling of two given spacecraft.
The apparatus which have heretofore been used for coupling spacecraft have generally been intended for docking rather than berthing. These prior art docking mechanisms are designed to approach their respective counterparts within a prescribed angle and direction. A nominal approach is one in which the docking mechanisms are aligned along a common axis so that the approach vector is normal to the plane of the coupling interface. However, the coordinated movement of two spacecraft along perfectly coincident bearings and at prescribed relative velocities or closing rates is a task which is very difficult to achieve. As a result of these operational considerations, known docking mechanisms are provided with alignment guides and impact attenuation devices around their entire circumference in order to accommodate the effects of vehicle misalignment and excessive closing rate, resulting in a relatively heavy and complex structure. These known docking apparatus are therefore expensive to manufacture, more prone to mechanical failure due to their complexity, and heavy as a result of all of the components they carry, thereby adversely affecting the payload-carrying capacity of the spacecraft to which the apparatus are mounted. For all of the foregoing reasons, berthing apparatus which are generally less mechanically complex, lighter in weight, and less expensive to manufacture than comparable docking mechanisms known in the art, are becoming increasingly more desirable for use in spacecraft coupling procedures.
Missions in space which will require the use of spacecraft coupling apparatus, particularly berthing apparatus, are currently in the planning stages. It is envisioned that, in the near future, the Space Transportation System (also referred to as the Space Shuttle Orbiter) developed in the United States by the National Aeronautics and Space Administration (NASA) will be used to service large, free-flying spacecraft, such as the proposed NASA Space Station and the Industrial Space Facility (ISF) developed by Space Industries Incorporated. Such spacecraft will be assembled and resupplied on orbit and will therefore require spacecraft coupling operations to be carried out on a frequent basis. Spacecraft coupling through the use of corresponding berthing apparatus is desirable, for it permits the precise alignment and coupling of one or more separate spacecraft with another spacecraft in a readily controllable manner. During the nominal operation of the Shuttle vehicle, berthing maneuvers will become more expedient through the use of a remotely controllable spacecraft positioning device such as the Remote Manipulator System (RMS), which is capable of grasping and maneuvering a free-flying spacecraft having a spacecraft berthing mechanism mounted thereon into engagement with a corresponding berthing mechanism mounted on another spacecraft, such as the Shuttle vehicle itself or one of the components of a space facility to be assembled.